Personal computers (PCs), sometimes referred to as micro-computers, have gained widespread use in recent years, primarily, because they are inexpensive and yet powerful enough to handle computationally-intensive applications. PCs typically include graphical user interfaces (GUIs). Users interact with and control an application executing on a PC using a GUI. For example, the Microsoft WINDOWS.TM. Operating System (OS) represents an operating system that provides a GUI. A user controls an application executing on a PC running the Microsoft WINDOWS.TM. OS using a mouse to select menu commands and click on and move icons.
The increasingly powerful applications for computers have led to a growing use of computers for various computer telephony applications. For example, voice mail systems are typically implemented using software executing on a computer that is connected to a telephone line for storing voice data signals transmitted over the telephone line. A user of a voice mail system typically controls the voice mail system using dual tone multiple frequency (DTMF) commands and, in particular, using a telephone keypad to select the DTMF commands available. For example, a user of a voice mail system typically dials a designated voice mail telephone number, and the user then uses keys of the user's telephone keypad to select various commands of the voice mail system's command hierarchy. Telephony applications can also include a voice user interface that recognizes speech signals and outputs speech signals.